Method of reclaiming molding and core sand



p 11, 1945. B. A. SMITH 2,384,573

METHOD OF RECLAIMING MOLDING AND CORE SAND Filed Aug. 29, 1942 4INVENTOR.

BENJAMIN A. SMITH ATTORNEYS Eatented Sept. 11, 1945.

UNITED STATES PATENT OFFICE METHOD OF RECLAIMING MOLDING AND CORE SANDBenjamin A. Smith, Rocky River, Ohio, assignor to The C. 0. Bartlett &Snow Company, Cleveland, Ohio, a corporation of Ohio Application August29, 1942, Serial No. 456,671

3 Claims.

This invention relates as indicated to a method of reclaiming orreconditioning foundry sand such as is used for molds and cores. Morespecifically, this invention is concerned with a process wherein thesand is heated to substantially a red heat for the purpose of drivingoff carbonaceous material and the like which may occur as an impurity inthe sand, after which the sand is cooled to room temperature in such away that there is a minimum amount of damage to the sand, and to alsoprovide that the sand, when discharged, will contain substantially thecorrect amount of moisture necessary to be present for the properhandling of the sand in the molding operation in which it is to be used.

The process of reconditioning foundry sand involving the step of heatingthe same to a red heat for the purpose of driving off any impurities,such as carbonaceous material, may be roughly divided into two parts-theheating stage and the cooling stage. The crystalline structure of thesand is such that it may not be subject to very sharp temperaturechanges since any such changes tend to set up in the sand grainsinternal stresses which may even proceed to a splitting of the sandgrain into small particles. If, however, the proper degree of care isexercised, both in heating and cooling the sand, it may be safely heatedto a red heat and then cooled to room temperature without anysubstantially adverse effects on the sand.

It is a principal object of my invention to provide a process of thecharacter and for the purposes described. Other obiectsof my inventionwill appear as the description proceeds.

To the accomplishment of the foregoing and related ends said inventionthen consists of the steps hereinafter fully described and particularlypointed out in the claims.

The annexed drawing shows one form of apparatus capable of performingone form of my improved process, and the following description setsforth in detail one approved mode of carrying out the invention, suchillustrated apparatus and disclosed method, however, constituting butone of the various ways in which the principle of my invention may beused.

In said annexed drawing, the single figure is a vertical sectional viewthrough a plant constructed so as to be capable of carrying out theprocess of my invention.

Before proceeding with a description of the process comprising myinvention, it is believed well to refer briefly to the construction andmode of operation of the apparatus illustrated in the drawing and bywhich such process may be performed.

Referring more specifically to the drawing, the same comprises a heatingkiln generally indicated at I, and a cooling kiln generally indicatedat'Z. The heating kiln comprises a tubular metallic shell 3substantially cylindrical in shape, and internally provided with arefractory lining l. The shell I carries axially spaced annular bearingrings 5 and 6 which revolve on trunnion rolls fitted with shaftsJournalled in bearing blocks as shown at I and 8 for the purpose ofrotatably supporting the kiln I in an inclined position. Secured to theshell 3 is a bull-ring 9 which cooperates with gearing and speedreduction means, generally indicated at I0 and a motor I I in rotatingthe kiln 3 about its longitudinal axis on its trunnion roll and bearingassemblies I and 8.

The upper end of the kiln I projects into a breeching or smoke box I2through which projects a feed chute II, the lower end ll of whichprojects into the kiln I. Material to be fed to the kiln is introducedthrough the open upper end I5 of the chute I3. A stack I6 is providedfor the purpose of carrying oil the products of combustion which areproduced within the kiln. An air seal shroud I1 is arranged about theupper end of the kiln I, closing the space between such kiln and thestack, but, at the same time, permitting relative rotation therebetweenwhile avoiding any appreciable infiltration of air.

Mounted adjacent the lower end of the kiln I is a firing hood I8likewise provided with a shroud I9 ail'ecting a substantiallyfluid-tight seal be tween the firing hood I 8 and the kiln I as thelatter rotates.

The firing hood I8 carries a conventional burner 20 adapted to utilizeany conventional fuel such as gas, oil, or powdered coal. Mounted at alevel chute 21 is arranged to carry by gravity the sand discharged fromthe lower end of the heating kiln I and to introduce the same throughthe opening 28 into the upper end of the cooling kiln 2.

The space about the cooling kiln 2 is laterally The shell 2| is, bymeans of bearing rings A transfer i kiln I.

'ual sand particles.

confined by means of a housing 29 at intervals provided with vents 30leading to an exhaust duct 3|. Mountedin the upper portion of the casingY 29 are a plurality of water feed devices 32, connected to a. commoninflow manifold not shown, and effective to cascade cooling water overthe outer surface of the shell 2| as the latter rotates. The steam andwater vapor generated in the housing 20 pass out through the stack 3|and the water in liquid form flows along the inclined surface of thefloor 33 to be discharged to the Bump N.

A stationary housing encloses the lower end of the kiln 2, and into suchhousing projects a screen extension 38 which is fastened to and rotateswith the shell 2|. 7 The flnes passing through the screen 36 aredischarged through the hopper 31 and the coarse material passing overthe screen is discharged through the chute 38.

, In carrying out the process of my invention, the sand to beconditioned, which is usually at a room temperature of about 60 R, willbe introduced through the charging chute l3 into the heating The rate offuel consumption, together with the rate of feed and those other factorswhich it may be necessary to adjust, such as the speed of rotation ofthe kiln, will all be so coordinated that the sand will pass through thekiln in a period of about 30 minutes and will be discharged from theheating mm at a temperature from 1400 F. to about 1600 F.

At this point it may be desirable to indicate that a convenient size ofapparatus for commercial use comprises a heating kiln, the metallicshell of which is about five feet in diameter and about twenty flve feetlong, having a six-inch thick refractory lining, making the net diameterof the heating'kiln about four feet. When the kiln is supported at aslope of about one-half inch per foot and rotated at a speed on theorder of about .8 to about 1.5 and at preferably about 1.0 R. P. M.,approximately flvetons of sand per hour will pass through the kiln.

After the sand, at a temperature of about 1400 F. to about 1600 F., isdischarged from the heating kiln I, it is carried by means of thetransfer chute 21 to the upper end of the cooling kiln.

, In order to economically match the heating kiln a slope to thehorizontal of about one-fourth inch a per foot and driven at a speed ofabout one to three and preferablyatabout two R. P. M. Under suchcircumstances, and when the exterior of the cooling kiln is flooded withwater in the manner hereinafter more particularly explained, the time oftravel through the cooler will be on the order of about 30 to 50minutes, averaging about 40 minutes.

The flights 22 are shallow, solid, angle projections which extendradially inwardly of the shell 2| for a distance just sufncient so as toinsure that the mass of sand in thecooler will roll and tumble withinthe revolving shell, rather than slide as a body over the innerperiphery of the 'shell 2| as the latter is rotated. Lifting flights soconstructed and arranged will result in a gentle asitation and mixing ofthe sand as it passes through the cooler, thus avoiding violentcasceding which might be destructive of the individnozzles or preferablyindividual boxes into which a supply of water is continuously fed, andfrom which the water flows over a weir onto the outer surface of theshell. The water used for cooling the shell exteriorly is .recirculated,i. e., that collected in the sump-34 being pumped back to thedistributing means at the hotter portions of the cylinder 2|, there toevaporate. The cool water supply fed in to replace evaporation losses isfirst fed through the distributors 22 at the lower or cooler end of thecylinder 2|. Depending upon the temperature of the water, it may benecessary to make adjustments in the rate at which it is fed to theouter surface of the shell.

At this point it should be noted that for best results the rate of flowof water over the shell 2| should be such that the outer surface of theshell at the hot end will have a temperature of about 500 F. to about600 F., and the temperature of the cold or lower end will be about F. toF. When conditions are maintained as above indicated, the sand will bedischarged from the lower end of the cooler at a temperature of about F.to about F.

Heating-the sand to the temperatures indicated may cause someagglomeration due to various causes so that it becomes necessary toscreen these agglomerated masses from the fines, and to this end thescreen II is provided.

when sand has been thus heated to the temperatures indicated above itwill be freed of substantially all moisture. However, a certain amountof moisture is necessary and desirable in molding sand, and this factmay be utilized to advantage in a refinement of my process as aboveexplained. It has been found that sand particles, after they have beencooled to approximately 500 F., may have water introduced theretowithout very substantial degradation of the sand particles. It is,therefore, within the contemplation of my invention to introduce waterby means of a spray, 39, into the cooler 2 at the point where the sandin its longitudinal travel through the cooler reaches a temperature ofabout 500 1''. A portion of the water thus introduced will, of course,be vaporized and the amount of water vaporized will have a substantialcooling effect on the sand and water which remains. The amount of waterthus introduced to the sand may accordingly be adjusted for bestresults. However, the end point which determines the amount of water tobe thus introduced is the amount of water which the sand may contain andwhich it will preferably contain for the molding operation in which itis to be used.

It is an important feature of my invention that I which carries it awayis not simply conduction,-

but a very complex heat transfer process involving radiation, conductionand convection, all to a degree and in different parts of the transfer.

For example, the heat in the center of the sand grain flows to theexterior of that grain purely by conduction. The temperature of theexterior surface of the sand grain is lowered and heat flows from it byradiation to the cool wall of the enclosing cooler cylinder. The heatflows from this wall surface by conduction through assure the metal wallof the cooler cylinder to the opposite side, where it is removed byconvection of the flowing water past this surface or by evaporation ofthe water which tended to wet the surface, the action here beingcombined evaporation and vapor convection. Some radiation of heat doestake place from the exterior wall of the cooler cylinder to the water,and to the water vapor forming as a result of the evaporation of some ofthe water, but this eifect is small.

It is also true that a minor portion of the heat of the, santiparticleis conducted through the interface between the sand particle and itscontact with the interior of the cylinder wall, but the area of suchinterface is generally so small (1. e. the point of contact is almostinfinitesimal) that only a small proportion of the total heat exchangetakes place in this manner. It will be observed, however, thatsubstantially all of the heat abstracted from the sand is at one stageforced to pass by conduction through the wall of the cylinder 2|. Thewall of the cylinder hence acts as a sort of thermal barrier against toorapid a rate of heat transfer away from the sand. Thus the sand grainsare cooled so slowly and evenly throughout their individual mass that nosubstantial portion of the sand is subjected to shock chilling. In thisway the generation of destructive contractlve forces in the sandparticles is avoided, thereby resulting in very minimum degradation ofthe sand particle size. I

The atmosphere is excluded fromthe cooler, i. e. no drafts ofatmospheric air are permitted to strike the sand since even such draftswould have the effect of causing a degradation of the sand particles onthe surfacebf the mass with which such drafts come in contact.

While the drawing is illustrative of one form of apparatus which may beused in carryin Ont my process, other types of apparatus may be for thesame purpose so long as the fundamentals of the process as above recitedare observed and maintained.

Other modes of applyin the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

I, therefore, particularly point out and distinctly claim as myinvention:

" and the like which comprises gradually heating the same to atemperature of about 1400" F. to 1600 F. and then simultaneouslyagitating and slowly cooling the same to a temperature of about 500 F.in a chamber from which the major portion of the heat is abstracted byconduction, and then applying water to the sand in an amount such thatthe residue in the sand after further cooling to room temperatureprovides substantially the required moisture content for its desireduse.

3. The method of conditioning foundry sand and the like which comprisesgradually heating the same during a period of about 30 minutes to atemperature'of about 1400 F. to 1600 F., and then simultaneouslyagitating and slowly cooling the same to a temperature of about 500 F.in a chamber substantially closed to the at- 'mosphere and from whichthe heat is abstracted by conduction through its wall, to the exteriorsurface of which water is applied, and then applying water to the samein an amount such that the residue in the sand after further coolingprovides substantially the required moisture content for its desireduse.

BENJAMIN A, sMrrH.

